The present invention relates to a noise reducing improvement within a hydraulic pump. More particularly, the invention is directed toward a configuration of a valve face on a cylinder head for providing periodic communication of piston bores in a rotating cylinder barrel with inlet and outlet passages.
The hydraulic pump or translator unit of the present invention is particularly contemplated for use in applications such as implement control where the pump is employed in combination with a coventional hydraulic motor. A prime mover or engine is coupled in driving relation with the pump while an output means is coupled with the motor. Hydraulic units of this type are commonly employed in a variety of applications to provide variable fluid transmission between the prime mover and powered equipment such as material handling machinery.
Within such a unit, the pump necessarily develops very high fluid pressures in order to operate the hydraulic motor. Pistons within the pump reciprocate between opposite limits of displacement as they are intermittently communicated with inlet and outlet passages. As the pistons reach a limit of reciprocation commonly referred to as "bottom dead center" and begin to move in the opposite direction, fluid pressure within the piston bore tends to be relatively lower than pressure in the outlet port. Upon subsequent communication with the outlet port, fluid tends to flow at a very high velocity in order to equalize pressures referred to above. This high speed flow tends to produce undesirable noise or "knocking" which may also undesirably affect operation of the pump.
It has been known in the prior art to employ either check valves or bleed slots to more nearly equalize pressure in the cylinder bores just prior to each bore entering into communication with an outlet passage in the cylinder head. Although both of these methods suitably reduce noise, they have also been found to exhibit certain deficiencies.